Okay so I imprisoned wuunferththe courtmage, but when I go to talk to him he tells me to go to the stone quarter and watch for the real killer, but as I make it halfway through the keep of windhelm, the quest suddenly updates and says chase the killer!! And when I go to kill calixto, he is invincible and can't be killed, even in hjerim. What do I do?? I have no previous saves and I have tried over and over again with the same results